Tuberculosis (TB) remains a leading cause of infectious mortality worldwide. At present, the only available vaccine for TB, Bacillus Calmette-Guirin (BCG), has not proven effective in the prevention of adult tuberculosis. As a result, an improved vaccine for TB is urgently needed. We have recently identified and characterized human, Mycobacterium tuberculosis (Mtb)-reactive, CD8+ T cells restricted by the non-classical (HLA-Ib) molecule MR1. This molecule has not previously been shown to present pathogen associated antigens. T cells restricted by MR1 often use a specific T cell receptor (TCR; V17.2).These cells have been termed Mucosa Associated Invariant T Cells (MAIT). Furthermore, we have also found that lung epithelial cells can be infected with Mtb, and are efficiently recognized by CD8+ T cells. The specific aims of this proposal are focused on developing an improved understanding of the role that the airway plays in the control of infection with Mtb. We have recently found that MR1-restricted MAIT are capable of recognizing Mtb as well as a variety of other pathogens, and that these and other CD8+ T cells are capable of efficiently recognizing Mtb-infected epithelial cells. At present, the role of airway epithelium in the host response to infection with Mtb remains relatively unexplored. In the first aim the full spectrum of pathogens recognized by MAIT will be characterized with regard to TCR usage. We postulate that the limited TCR usage will correlate with limited diversity with regard to pathogen discrimination. The second Aim will define the intracellular location of Mtb in epithelial cells, and will define critical components in the antigen processing and presentation pathway. Here, we postulate that the immune system has evolved mechanisms to sample the intracellular environment of Mtb. Finally, we will address the role of iNOS in the direct control of Mtb growth. Here, we postulate that the major role of iNOS in humans resides at the level of the lung epithelium. PUBLIC HEALTH RELEVANCE: Tuberculosis remains a leading cause of infectious mortality worldwide, and is caused by a bacterium that resides inside of cells. In order for the immune response to respond to the infection, it must identify those cells that harbor the bacterium. Cytotoxic T cells are uniquely poised to perform this function. The goal of this research is to understand how these cells can recognize infected cells, and how this leads to control of the infection.